CC resistor drift in princeton reverb

[texwest]

Hey guys!  I'm working on a guys 68 princeton reverb.  Nearly every resistor in the amp is 20% off.  The plate resistors are around 120k, the input 68k's are 40k in parallel, the cathode resistors are 2k, etc.   Wondering if you think it's a good idea to replace those or not? 

I'm thinking about definitely replacing the 1.5k and other cathode resistors because I'm replacing those caps.  Thinking about leaving the plate and input resistors.  What do you think?

The amp has all sorts of other issues and sat in a barn for years so the cabinet and speaker are destroyed.  Incredibly, it does make sound in spite of a huge amount of rust on the transformers.

thanks

[pdf64]

Whichever way you go is open to criticism.
I suggest to consult with its owner; if something’s out of spec but not actually causing a functional issue, what does he want you to do?

[HotBluePlates]

IMO, the precise values don't count for much.  If the amp sounds good, then it is good.

The best sounding vintage Princeton Reverb I ever owned had preamp cathode bypass caps that dropped in value to as low as 1µF.  I foolishly "repaired" the amp to be like-new with all new 25µF caps.

I realized later that in most blackface/silverface Fender amps I get much more low end than I really want, and tend to keep the Bass control down around 1-2.

[Ethan]

Considering how far CC resistors can drift and considering how that amp was stored, it's remarkable that the values only drifted 20% which is, technically, within spec.

Guitar amp circuits, especially many older ones, provide an enormous amount of leeway in terms of parts value variance.  I agree with the others; leave it as it is and see where you stand.  You can always replace parts or change values later if there's a problem.  You're likely to run into more issues (noise) resulting from moisture than you will from drifting values.  Do be sure to gently brush the rust off of that iron and seal it with some spray paint to prevent further damage!

[texwest]

Yeah this amp was sounding terrible when I got it, so there is no baseline really.   It was humming absolutely terribly because the bias cap came loose.  And you could hear AC ripple because of that too.  I'm thinking if they are more than 20% then I will replace them.

thanks for your help

[PRR]

...Nearly every resistor in the amp is 20% off....

Change the battery in your meter.

Yes CCs drift. But not all the same amount.